A centrifugal separator consists of a separation drum which is rotated at high speed. Liquids separate into zones within the drum due to their differing densities. An example of an application of centrifugal separation is in oil/water separation. Upon rotation of the centrifugal separator water migrates to the sides of the rotating drum while the lighter oil forms an oil zone which floats upon the water. In order for centrifugal separation to be attained a constant oil/water interface is required. With a constant oil/water interface, oil accumulations are skimmed from the surface of the water by passing from the drum through a spillway form of oil outlet. Any water which is "excess" to that required to maintain the interface is removed through a water outlet.
One of the most difficult aspects of centrifugal separation is achieving the constant interface between two liquids being separated. If a constant interface cannot be achieved, it is only a matter of time before one liquid starts flowing from the outlet intended for the other liquid. Each adjustment of the liquid interface takes hours as the centrifugal separator must be taken apart and alterations made to an interface assembly within the interior of the drum. The relative percentage of liquids varies widely, so considerable time and effort must be spent on interface adjustment each time the liquids being processed originate from a different source.